Please refer to FIG. 1, which is a circuit diagram showing a light detector array of an input display according to the first prior art.
In FIG. 1, each unit of the light detector array includes a TFT switch. For example, the operation of the unit 11 in the position where the first read-out line intersects the first gate line is as follows. When the light detector array is OFF, the gate line 1 is at low voltage. The body diode of the TFT is reversely biased so that there is no current flowing through the TFT. When the gate line 1 turns to high voltage, the current flows from gate line 1 through read-out line 1 to the readout amplifier 12.
A photo-induced ON current occurs when the light is emitted onto the TFT. When the light is emitted onto the TFT, the photo-induced ON current increases. Contrarily, when no light is emitted onto the TFT, the photo-induced ON current decreases.
When the input display with the light detector array is used, the touch of the display will influence the quantity of the incident light. Hence, which position of the display has been touched is able to be detected by sensing the quantity of the photo-induced ON current.
However, the drawback of the input display with the light detector array is the generation of the photo-induced leakage current, which also occurs when the light is emitted onto the TFT. The sensing and the detection of the display are seriously held back by the photo-induced leakage current.
To overcome the drawback, another implementation of the display has been provided. Please refer to FIG. 2, which is a circuit diagram showing a light detector array of an input display according to the second prior art.
In FIG. 2, each unit of the light detector array includes two TFT switches. The unit 21 in the position where read-out line #1 intersects gate line #1 is taken for example. The switch-TFT 11 is arranged for switching and the photo-TFT 11 is arranged for detecting the intensity of the incident light.
In FIG. 2, the additional TFT is unnecessary to be emitted by the incident light, so the photo-induced leakage current is able to be decreased. However, the increased number of TFT results in a lower process yield.